In recent years emphasis in biomaterial engineering has shifted from biostable materials to biodegradable materials that can degrade to non-toxic products under physiological conditions. Polymers of lactic and glycolic acid and their copolymers poly(lactide-co-glycolide), (PLAGA) are some of the most commonly used biodegradable polymers for medical applications. All these polymers are associated with some limitations, which demand the search for novel biodegradable materials that are biocompatible and bioresponsive. Biodegradable polyphosphazenes, a unique class of inorganic polymer developed recently have the potential to become ideal candidates for various biomedical applications due to their unprecedented synthetic flexibility and versatile properties. PI had previously shown that blending polyphosphazenes with PLAGA can significantly preclude the accumulation of acidic degradation products of PLAGA and associated inflammatory reponses, at the same time can significantly improve their mechanical properties and osteoconductivity. We believe that the synthetic flexibility of polyphosphazenes will allow the design of novel macromolecules, which can for miscible blends with PLAGA and increase the bioactivity. These novel blends due to their well-tuned biodegradability, mechanical and biological properties combined with osteointegrity can serve a variety of needs in orthopaedics. This goal will be achieved via the following specific aims: Specific Aim 1: To design, synthesize and characterize novel biodegradable polyphosphazenes, which can form miscible blends with PLAGA as candidate materials for bone tissue engineering. Specific Aim 2: To construct novel blends of polyphosphazenes with PLAGA and perform optimization studues with these blends focusing on improvements in physico-chemical properties, mechanical properties, in vitro degradation, in vitro mineralization and osteoconductivity. Specific Aim 3: To perform biological evaluation of novel blends of polyphosphazenes with PLAGA using in vivo animal models.